Recovery of hydrocarbons



OcLS, i945. G. H. SHORT RECOVERY OF HYDROGARBONS Filed Feb. 10, 1942 m mPZmUZOU ZUJOE INVENTOR GRAHAM H. SHORT HOlVHVdIS HBG'IOH SVQ TIIT Patente-d Oct". 9, 1945 RECOVERY OF HYDROCARBONS Graham H. Short, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application February 10, 1942, Serial No. 430,267

2 Claims.

This invention relates to an improved process for the recovery of hydrocarbons from hydrocarbon fluids containing the same and from metal salt complexes thereof. More particularly, it relates to an improved method for recovering diolens in substantially pure state subsequent to selective chemical absorption from hydrocarbon fluids by means of metal salt reagents. Still more specifically, the present invention has application as a step in the process of isolating and/or purifying conjugated diolefin hydrocarbons of the butadiene type through the intermediate formation of complex addition compounds with metal salts including cuprous halides.

In the separation of aliphatic diolens from complex hydrocarbon mixtures containing parafns and olefins of similar boiling points, the thermally-reversible reaction between said diolens and certain inorganic salts of monovalent heavy metals of Groups I and II of the periodictable is often'utilized. With said inorganic salts, and particularly with cuprous halides such as the chlorideor bromide, addition complexes may be formed which are separable from the hydrocarbon mixtures and which may be dissociated by simple treatment such as moderate heating to recover the dioleln.

The utilization of cuprous halide reagents to labsorb diolefins involves the contact of the diolen-containing hydrocarbon iiuids with the metal salt in a liquid medium or in solid form at temperatures and reaction times which favor the formation of the diolen-cuprous halide addition complex. This latter product being relatively insoluble in any solvents present is then segregated by suitable accessory means, or by the reagent itself in the case of solid-type reagents.

Following this segregation of the intermediate reaction product, the diolefin is recovered by heating the additionv complex to decomposition temperatures and collecting the evolved dioleiln` (Cl. ZBO-681.5)

ride with substantially non-adsorbent materials. Such reagents'oier distinct advantages from the standpoint of stability, favorable reaction times, and more selective absorption of diolens. Also,

since the dioleiin addition complex is retained s This is apparently due to adsorption of' unre- The purityl of the dioleiin thus recovered deinated by evacuation of the reagent bed and/or, the zone containing the diolenaddition complex,`losses of diolen are often occasioned by premature decomposition of said complex. Also, the provision of sub-atmospheric pressures for large vessels in commercial installation is both expensive and hazardous because of possible air contamination. f

I have now discovered a method for conducting the diolefin desorption step in processes of yield of a purer product under more-efiicient` These and more easily controlled conditions. and other objects yand advantages of my process including the avoidance of subatmospheric pres-r sures will'belevident from the following disclos'ure.

In general the process of-my invention contemplates the lpurication and decomposition of a diolen-metal salt addition complex, which has beenformed by addition-reaction with ,a'fs'olid f complexforming metal salt' reagent withya' suitable diolen in order to recover thediole'n' in a high state of purity. Preferably, .the diolefin butais of the conjugated type exemplified by diene, isoprene, piperylene,l etc.

In one specific embodiment my process comprises the steps of removing mechanically-retained unreacted hydrocarbons from a cuprous halide reagent bearing a diolen addition com-` plex by the passage therethrough ol a substantially non-condensible flush gas at temperatures treating hydrocarbons in either liquid or vapor f phase through cuprous chloride reagent in a veslsel connected for either upward or downward flow. Assuming that a C4 hydrocarbon mixture is being treated in vapor phase and withupward flow through the reagent, the feed entering through line -I passes through vaporizer 2-and thence through valve 4, and lines Sand 6 to the reagent vessel 1. This vessel which may be an elongated tower or a number of relatively small diameter "tubes is jacketed with a heat exchange medium in jacket I5, and during diolen absorption a cooling medium is circulated to maintain optimum absorption temperatures.

The hydrocarbon vapors after passage through vessel 1 exit through line 8, valve 9 and line I0 with the absorbed diolen being retained by the cuprous chloride reagent. When downward flow is being utilized the corresponding flow of hydrocarbons is through valve. II. line I2, line 8 and through the vessel 1, with the diolefin denuded fluid exiting through line 6, valve I3 and line I4.

After a predetermined amount of diolen has been absorbed by the reagent in vessel 1 with the formation of diolen-cuprous chloride complex. the hydrocarbon feed is either stopped or diverted to a second reagent vessel While the diolen is recovered from vessel 1. The rst step in this procedure is the removal of unreacted hydrocarbons from the reagent and the reagent vessel. A chemically inert, non-condensible flush gas of the type described below is admitted through pressure regulating valve I6 and passes through line 6, vessel 1, line 8, valve 8 and line i0 to avent line which may include recovery apparatus for C4 hydrocarbons if desired. This gas may be supplied through line I1 from an unrelated source (not shown) or it may be furnished fromgas holder I8 by means of blower I9 and line 20. This latter arrangement is of particular use during dioleiin desorption as will be explained below. While this llush gas is passing the cooling medium is usually withdrawn from jacket l5, although in some cases the temperature in the vreagent vessel is not allowed to rise very much above absorption temperatures. With the butadiene-cuprous chloride complex on the reagent, temperatures in the neighborhood of 80 to 100 F. may be reached while passing the flush gas to remove adsorbed, unreacted hydrocarbons.

When the flushing is complete, as can be determined by tests for condensate in the etlluent gas stream, the desorption of dloleiin is begun by introducing a heating medium such as steam or heated water into jacket I5. When decomposition temperatures are reached evolution of gas- Y ecus diolelin commences, and during this period,

the flush gas is passed through the vessel and, by closing valve 21 in exit line II)` through valve 2|, condenser 22 and line 23 to separator 24. The separator gas may be vented through valve 28, or preferably may be recycled through valve 25 to supply vessel I8. In the latter arrangement, it is picked up by blower I9 and passed through line 20 to the admittance valve IB.

Valve I6 is usually regulated to maintain a constant low superatmospheric pressure on the reagent vessel and on the condensing and separating system, and as diolen desorption begins with decomposition of the diolefln-cuprous chloride complex, the gas volume is proportionately decreased. The gaseous diolen is condensed `in condenser 22 and removed from separator 24 through line 2S to storage. Near the end of the desorption, the gas volume from Valve i6 again increases, and the last traces of diolen are rapidly removed from the reagent bed and are recovered. The reagent is then cooled and is ready for further service in diolen absorption.

Many modifications ofthe arrangements described may bemade within the terms of my invention. Thus, additional heating and/or cooling means may be installed in the ush gas line to facilitate the heating and cooling of the reagent be'd. Or the ush gas may be recycled even prior to desorption provided that the nondiolenic hydrocarbon contaminants flushed from the reagent are not retained in the recycled gas stream. Contaminants such as Cs and C5 paraffins and olefins and the like may'be removed from the gas stream by compression and/or absorption methods similar to natural gasoline recovery operations.

Also, while the drawing shows the desorption step operated with both ush gas and diolens removed from the top of the reagent vessel, this ilow may be reversed or alternated, if desired. Or, in treating liquid hydrocarbons the ilushing step may be downward to obtain a certain degree of gravity drainage, while desorption may be conducted from either end of the reagent vessel. These and other modifications will be obvious from the accompanying disclosure.

The lengthof the flushing period may vary somewhat with the boiling range of the feed stock and the nature of the reagent. A-reagent which consists of an adsorbent carrier such as bauxite, charcoal or silica gel bearing cuprous chloride may retain a much greater amount of either liquid or gaseous hydrocarbons than one consisting of a substantially non-adsorbent material such as asbestos or cellulose fiber or sawdust mixed with cuprous chloride. The volume and rate of flow of the ush gas is ordinarily selected in ac- Y cordance with these factors to give substantially complete removal of the unreacted mechanically adsorbed hydrocarbons in the shortest feasible period in order to rapidly complete the desorption step and prepare the reagent for absorption serv- Y ice.

The temperatures during the ushing period are regulated well below those causing complex l Of course, once the gas stream is directed' Ordinarily temperatures are.

halide complex by heat, the rate of decomposition is affected by both the temperature and the pressure. With the butadiene-cuprous chloride complex, very rapid decomposition occurs at temperatures of 180 to 210 F. and at atmospheric pressure. Small increases in the pressure such as the values of l to pounds gage I have found useful during desorption may .cause slight increases in the temperatures required for equivalent decomposition rates. However, desorption is satisfactorily rapid at temperatures not usually exceeding about 210 F., particularly since the initial and iinal stages are appreciably shortened by the passage of flush gas during the lentire operation. With other complexes such as the isoprene andpiperylene compounds, desorption temperatures are generally lower, but the same principles are applicable to the steps of diolefn recovery.

By maintaining a relatively constant superatmospheric pressure during the desorption step,

I am able to effect a much more uniform rate' of diolen evolution and to control the recovery of diolen liquid in a more satisfactory manner. The increased pressure is of great benet in the condensation of the evolved vapors, particularly in the case of butadiene. Thus, the rate and extent of cooling in the condenser is reduced. and excessive refrigeration is avoided without any losses of valuable product. Further, any traces of diolen carried in the recycled gas stream would be eventually recovered by this arrangement.

Pressures during the ushing and desorption steps are usually only slightly above atmospheric,

and sufficient to prevent inward leakage of air into vessels, valves, and lines and connectons. When treating C4 hydrocarbons to recover but-adiene these pressures may range from zero to 15 pound gage or even higher with a maximum of 10 to 15 pounds gauge usually preferred. When mixtures to be treated comprise C5 or higherboiling hydrocarbons, similar pressures are suitable for the desorption step, although substantially atmospheric pressures are often employed in the flushing step to remove the less volatile constituents at lower temperatures.

The gases which are suitable for my process are those substantially non-condensible at the pressures and temperatures employed and easily separable from diolen condensates. These gases are also substantially oxygen-free and inert toward the hydrocarbons and the absorption reagents under all the conditions employed. Specific examples are, nitrogen, carbon dioxide, methane, ethane, or natural gas mixtures containing major proportions of methane. Obviously mixtures of these gases are suitable, and when nat-' ural gas compositions are employed, reactive impurities are rst removed. Gases containing propane may also be used, as long as this higherboiling material does not condense or otherwise interfere with the separation of the liquid diolefln product. The choice of a ush gas will depend to a large extent on location and availability, and total recycling may be economical when nitrogen or similarly expensive mixtures are utilized.

The following specic applications of my process will serve to further illustrate its operation and advantages.

Example I A C4 hydrocarbon liquid containing butadiene along with some butane and major amounts of normal butenes was treated in liquid phase over a. reagent consisting of charcoal impregnated.

with 40 per cent by weight of cuprous chloride. The absorption was carried out at 40 F. and

when the reagent bed had absorbeda calculated quantity of butadiene, the ow was stopped, the liquid in the reagent vessel was vaporized at a temperature just above the absorption temperature, and methane 'gas at about 80n F, was passed through the bed until condensation tests showed substantially no'furthter removal of Cri-hydro- 5 pounds gage while the reagent was heated to" 200 F. The butadiene was rapidly and completely evolved and recovered with a purity of 991 per cent.

When the same reagent was desorbed after merely attempting to remove all the unreacted hydrocarbons by vaporization at F., the desorbed butadiene was only 75 per cent pure.

Example II A gas mixture of Ca and C4 hydrocarbons was treated over a reagent lconsisting of cuprous chloride and asbestos liber at a temperature'of 40 F. for the absorption of butadiene contained therein. After the reagent had become spent with respect to butadiene the now of hydrocarbons was stopped, and natural gas containing only traces of propane and no higher boiling material was passed through the reagent at 90 F. until no condensate was detectable in the eilluent gas stream. The reagent was then heated to 210 F. with the gas stream passing through a condenser and separatorl with a back-pressure of about 10 pounds gage. 'I'he gas was separated and vented, while the diolen condensate was recovered in substantially pure form.

Example III A mixture of butene-2 and butadiene, containing 15 volume per cent of diolen was treated in vapor phase over a reagent consisting of a mixture of cuprous chloride and oil-impregnated sawdust at 45 F. and substantially non-condensing conditions. The now of feed vapors was stopped when the reagent had accumulated nearly the maxium amount of diolefn addition complex and the reagent was desorbed at F. to recover a diolen concentrate containing 92 per cent butadiene.

After an identical absorption` step with the same charge and reagent, nitrogen gas was passed through the bed of reagent and diolefn addition complex at 90 F. and a ow of 0.5 gas volume per minute per volume of reagent until all condensible hydrocarbons were flushed from the reagent vessel. The ilushing gas stream was then passed through a condenser and separator with a back-pressure of one pound gage on the separator while butadiene was desorbed by heating'the reagent to 190 F. The nitrogen gas was recycled continuously during desorption, and the butadiene was condensed and separated with a purity of over 99 per cent.

While the foregoing exemplary operations have illustrated specic applications of my process numerous modications and extensions within the scope of' the invention are possible.

I claim:

1. In a process for the recovery of aliphatic conjugated diolcnnsfrom hydrocarbon mixtures containing the .sa-mc and close-boiling non-di- The reagent vessel olenic hydrocarbons of substantially the .same boiling range by intimately contacting said mixture with a reagent containing a cuprous halide and thereby causing said diolen to selectively react with said cuprous halide to form a solid diolen-cuprous halide complex mechanically retaining unreacted non-diclenic hydrocarbons, and thereafter desorbing the diolen from said solid complex by heating same to an elevated latter, carrying out said last-named step at at least atmospheric pressure and at temperatures 'below those causing appreciable desorption of diolen from said complex, thereafter effecting said desorbing step by passing through said mass of solid complex a stream of said inert gas while heating said complex to a, temperature suiciently high to effect desorption of said diolen therefrom and while maintaining substantially constant 10W superatmospheric pressure, removing the resulting mixture of diolen and said inert gas, and separating said diolen in `substantially pure form from said mixture by subjecting said mixture to conditions causing condensation of said diolen while allowing said inert gas to remain as such.

2. The process of claim 1 wherein said gas is methane.

GRAHAM H. SHORT. 

